Both xerographic printers and direct marking prints have the potential to produce streaky images. In xerographic printers, variations in the performance of the subsystems (exposure, charging, development, transfer, and fusing) across the process direction will lead to a development efficiency that is a function of cross-process position and consequently streaks. In direct marking printers, the drop size and direction can vary as a function of nozzle, also leading to streaks.
One approach to mitigate streaking is to sense the magnitude of the streaking and actuate a subsystem that compensates for the streaking. One approach to sensing the magnitude of the streaking is to put a linear array sensor inside the printer. The linear array sensor is focused on the image receiver in the printer, for example, a photoreceptor surface. In a direct marking printer this can be the image drum. The linear array can monitor the uniformity of a printed test pattern. The test pattern can consist of a series of strips of various colors and densities.
The sensor typically monitors the specular reflection off the substrate. When there is no toner or ink on the substrate, the light from the illuminator is specularly reflected into the sensor and the sensor response is large. When there is ink or toner on the substrate, the ink or toner scatters the light away from the sensor and the sensor response decreases. The more ink or toner on the surface, the smaller the sensor response is.
This disclosure provides a means for calibrating an image output sensor such as a linear array sensor.